As a method for manufacturing carbon fiber bundles, a conventionally known method is as follows: converting a carbon-fiber precursor acrylic fiber bundle (hereinafter, may also be referred to as a “precursor fiber bundle”) made of acrylic fiber or the like into a stabilized fiber bundle by heating the bundle at 200˜400° C. under oxidizing atmosphere (stabilization process); and carbonizing the bundle at 1000° C. or higher under inert atmosphere (carbonization process). A carbon-fiber bundle manufactured using such a method has excellent mechanical characteristics and is put into wide industrial applications especially as reinforced fiber for composite materials.
However, during stabilization and the subsequent carbonization process (hereinafter, a stabilization process and a carbonization process may be combined and referred to as a “heating process”) of such a method for manufacturing carbon-fiber bundles, problems may occur such as fuzzy fibers or yarn breakage because of single fibers fused during stabilization for converting a precursor fiber bundle to a stabilized fiber bundle. As a method for preventing single fibers from fusing, applying an oil agent composition on surfaces of precursor fiber bundles is known (oil treatment), and various oil agent compositions have been studied.
Generally used oil agent compositions are silicone-based oil agents whose main component is silicone, which is effective in preventing fusion among single fibers.
However, when silicone-based oil agents are heated, cross-linking reactions progresses to cause high viscosity, and such viscose material is likely to be deposited on surfaces of fiber transport rollers and guides used during a manufacturing process or during stabilization of precursor fiber bundles. Accordingly, the precursor fiber bundles or stabilized fiber bundles may become wound around or snagged onto transport rollers or guides and cause yarn breakage. As a result, operating efficiency may be lowered.
Moreover, during the heating process, a precursor fiber bundle with applied silicone-based oil agent is likely to produce silicon compounds such as silicon oxide, silicon carbide and silicon nitride, thus lowering industrial productivity and product quality.
In recent years, as an increase in demand for carbon fibers has led to a call for even larger production equipment and greater productivity, one of the issues to be solved is lowered industrial productivity caused by silicon compounds produced during the heating process such as those described above.
Accordingly, oil agent compositions that have reduced silicone content or do not contain silicone are proposed for reducing silicone content in oil-treated precursor fiber bundles. An example is an oil agent composition whose silicone content is lowered by adding 40˜100 mass % of an emulsifier that contains a polycyclic aromatic compound at 50˜100 mass % (see patent publication 1.)
Also proposed is such an oil agent composition containing silicone and a heat-resistant resin whereby the amount of remaining oil agent is 80 mass % or greater after being heated at 250° C. for 2 hours in air (see patent publication 2).
Other examples are an oil agent composition made of a bisphenol A aromatic compound and an amino-modified silicone (see patent publications 3 and 4), and an oil agent composition mainly containing a fatty acid ester of bisphenol A-alkylene oxide adduct (see patent publication 5).
Yet another example is an oil agent composition with a silicone content lowered by using an ester compound containing at least three ester groups in the molecule (see patent publication 6).
Moreover, by using a water-soluble amide and an ester compound containing at least three ester groups in the molecule, the silicone content is lowered while fusion of fibers is prevented and stable operating efficiency is achieved (see patent publication 7).
Further proposed is an oil agent composition containing at least 10 mass % of a compound having a reactive functional group without containing a silicone compound, or if a silicone compound is contained, its content is 2 mass % or lower in terms of silicon mass (see patent publication 8).
Yet further proposed is an oil agent composition which contains 0.2˜20 wt. % of an acrylic polymer having an aminoalkylene group in the side chain, 60˜90 wt. % of a specific ester compound and 10˜40 wt. % of a surfactant (see patent publication 9).